Devices for fastening rails such as railway rails or runways, are well known. They are preferably used by pairs, the devices of each pair being positioned opposite to each other, on either side of the foot of said rails, in order to fasten them to the surface of a preferably planar support.
According to the state of the art, a distinction is made between different types of fastening devices, fastening devices to be bolted and fastening systems to be welded. The present invention is more specifically set within the scope of fastening devices to be bolted, and even more specifically within the scope of so-called flexible fastening devices. The latter, which are also commonly called “fastening clips”, consist of at least two elements, so-called “primary element” and “secondary element”.
The “primary element” generally comprises two parts. The first part is supported on the support and is firmly fastened thereto. The second part allows confinement of the rail, and more particularly of the sole or the foot of the rail, for example by having an overhanging side surface which comes into contact with the sole or the foot of the rail.
The “secondary element”, which defines the type of fastening here, is a means for fastening the first and second parts to each other. Generally, the means for fastening comprise at least one screw, the head of which is introduced into an aperture present in the first and in the second element and onto which a nut will be fastened. Any nut and bolt fasteners, in particular including washer(s) which may be associated with them, are more globally grouped as secondary elements.
Further, it will be noted that the side surface of the second part of the primary element, which overhangs and comes into contact with the sole or the foot of the rail, may have an elastomeric nose. The presence of this nose allows some vertical flexibility, particularly adapted to absorbing the stresses induced by the passing of the rollers of the vehicles rolling along the rail. In other words, by means of these clips, the rail is not totally restrained, since it is firmly held sideways but it retains the capability of moving vertically within certain limits.
In certain cases, the primary element may also only consist of a single part, the screw (secondary element) then having to cross the support on which this part rests. The support, which most often is a metal beam, may be bored through for this purpose.
The use of a continuous rubber strip or pad, which is placed under the support of the rail, jointly with that of these clips, contributes to providing under operating conditions, a certain vertical flexibility of the rail and thereby obtaining a flexible fastening of the rail.
In order to obtain a proper assembly by which the required tightening may be guaranteed for perfect fastening of the rail to its support, it is imperative to position the fastening means very accurately.
The advantage of this type of systems is that it may be adjusted and relatively easily disassembled.
Further, this solution is particularly advantageous in the case of significant loads or in the case of particularly severe utilization rates as in the case of continuous operation of cranes.
For that matter, in the particular case of cranes or bridge cranes, this type of fastening further has certain technical drawbacks, related to the occurrence of new additional specific constraints for these applications.
Indeed, (harbor) cranes and bridge cranes are presently both heavier, higher and bulkier than previously. Further, they move and operate more rapidly. Comparatively, the number of wheels and their diameters do not increase in proportion, which has the effect of increasing the load per wheel of those cranes and bridge cranes.
Consequently it is seen that the rails and therefore the fastening systems are subject to new mechanical stresses, essentially from vibrations, to which they have to be able to respond.
In concrete terms, the vibrations cause rotation of the rail, which causes stresses and play at the fastening systems and thereby even wear or unscrewing of the parts.
To these mechanical stresses are added those generated by defects during laying (a poorly applied clip against the rail, bad engagement of the screw, . . . ) which also cause play to occur at the fastening systems and at the rail over elapse of time.